For over a century, hundreds of inventions have attempted to harness the vast amount of energy in waves. Due to scarcity of resources and energy, a lot of effort has been directed towards tapping into the vast amount of unharnessed natural resources. One such form of unharnessed natural resources is in the form of wave energy.
Ocean's waves contain more energy that can be harnessed than wind and solar energy combined. This energy is constantly available and oceans cover over 70% of the earth's surface.
It has been estimated that waves can contain as much as 70 KW of power for every linear meter of wave; therefore a 15 meter long wavefront can deliver over 1 MW of power if its energy could be exploited in a practical manner. Even more power can be harvested per meter wavefront of sideflow from adjacent waves is taken in to account.
The methods currently employed for extracting the wave's energy fall basically in to four main categories:                Point absorbers, which are buoys using the heaving motion of the waves that is being converted to mechanical and then electrical energy, or directly to electrical energy like Power Buoy of Ocean Power Technology.        Attenuators, like McCabe's Wave Pump or “Pelamis” which use a few floating bodies hinged together which are in relative motion to each other due to the passing waves. At the hinging point, hydraulic pistons push oil in hydraulic motors which in turn actuate electric generators.        Terminators, like Oscillating Water Column (OWC) employed in the “Mighty Whale” Japanese project or in various shore based projects like the one on the Pico island.        Overtopping, employed either on shore or on a floating structure like the “Wave Dragon” Danish project which also involves Germany, Sweden, The UK, and Austria.        
The first two categories employ mechanical devices that are inefficient and demand a high capital cost due to the demanding conditions out in the ocean. The seals needed, the inability to service on the spot, the dangerous conditions of even approaching the devices to be tugged for service make them undesirable as viable solutions. They also need a long “trial and error” validation period because they are not technologies that have stood the test of time.
The last two categories use the wave's energy to actuate air, and their water turbines actuate electrical generators. The current invention falls into this broad category, so this category will be further analyzed.
The OWC is mostly used on shores where a trapezoidal chamber communicates on the lower side with the sea water allowing the incoming wave to raise the inside level of water. When the wave retreats, on a through, the level of the water inside will drop. This raising and lowering of the water level inside the chamber acts as a piston, pushing and pulling the air above it through a narrow hole where a Wells turbine rotates, actuating an electric generator.
The Wells turbine, named after its inventor is a self-rectifying turbine, which rotates in the same direction regardless of the direction where the air is coming from. The advantage of this concept is a simple design that has no moving parts except the group of turbine-generator.
The disadvantages of this system are: low efficiency of the air turbine, a chamber of limited size which cannot be bigger than the order of magnitude of a wave which requires a separate chamber for each separate turbine-generator, chambers cannot be coupled to actuate one bigger turbine generator group, and lost kinetic energy of the wave because the separating wall of the chamber is always submerged.
The existing OWC systems are mostly placed on shore where the waves have already lost most of the energy they had in deep sea water. Also, the sites need to have a particular configuration, and typically involve expensive real estate.
Due to the fact that there is a significant period of time between waves and also because the wave's lowering is slower than the rising level inside the chamber, the Wells turbine tends to stall.
Another drawback is that because the air turbine is so noisy, this limits the number of sites where it can be implemented.
Overtopping is used on the “Wave Dragon”, which is a floating structure that has a ramp (artificial beach) on which the wave climbs due to its kinetic energy and spills over into a basin above the sea water level. Then the water falls through a water turbine and actuates an electric generator much like in a regular hydro power plant. This simplicity is an advantage of the “Wave Dragon.” Another obvious advantage of this design is the use of a technology that has long been used and perfected.
Water turbines which are suitable for this purpose have been used in low head river water power plants for many decades and have been developed to a high level of efficiency and reliability. In France the 240 MW La Rance tidal power station has been using such turbines in a salt water environment since 1967. Thus, in contrast to most of the WEC principles, a proven and mature technology can be used for the production of electrical energy.
Turbine operating conditions in a WEC are quite different from the ones in a normal hydro power plant. In the Wave Dragon, the turbine head range is typically between 1.0 and 4.0 m, which is on the lower bounds of existing water turbine experience. While there are only slow and relatively small variations of flow and head in a river hydro power plant, the strong stochastic variations of the wave overtopping call for a radically different mode of operation in the Wave Dragon. The head, being a function of the significant wave height, is varying in a range as large as 1:4, and it has been shown by Knapp (2005) that the discharge has to be regulated within time intervals as short as ten seconds in order to achieve a good efficiency of the energy exploitation.
A river hydro power plant which is properly maintained can have a life of 40-80 years. On an unmanned offshore device, the environmental conditions are much rougher, and routine maintenance work is much more difficult to perform. Special criteria for the choice and construction of water turbines for the Wave Dragon have to be followed; it is advisable to aim for constructional simplicity rather than maximum peak efficiency.
By stopping a number of turbines at lower flow rates, the flow rate can be regulated over a wider range without sacrificing efficiency. Single units can be taken out of service for maintenance without stopping production. Capacity demanded for hoisting and transport equipment to perform repair and maintenance work is greatly reduced. The smaller turbines have shorter draft tubes, and are thus easier to accommodate in the whole device. The smaller turbines have a higher speed, which reduces the cost of the generator. Another advantage of the Wave Dragon by being a floating structure is the possibility of being moored in deep waters where the energy of the wave is not diminished by the sea floor and there is no real estate cost involved.
There are quite a few important drawbacks of the overtopping devices, and in particular, the Wave Dragon.
The capacity of the water reservoir has to be significant to feed the turbine between two waves. It is 8,000 cubic meters which means over 8,000 tons of water to be lifted and held above the sea level in a precarious act of balancing. It is like a plate filled with water which easily will spill when shaken. The structure to hold all this weight becomes significantly bulky and expensive. The mooring lines and anchoring will have to be dimensioned accordingly mostly taking also in consideration the two floating wings that spread sideways to gather the waves giving a span of 300 meters to the whole structure.
Underneath there are pockets of air for lifting and lowering the structure such that always the ramp is at the proper height depending on the height of the incoming waves. If the ramp is too high, the incoming wave may not make it over or too little water will be added to the reservoir. If the ramp is too low, the water will just wash over the reservoir not giving enough head for the turbine.
A sophisticated “just in time” automation system will have to keep this huge structure in balance at all times since the level of the ramp has to continuously keep up with the surrounding conditions, the amount of momentary load (variations of thousands of tons of water weight of load on the structure in a matter of seconds between waves), the task of keeping an even keel, horizontal position at all times in choppy waters. The turbines are equipped with cylindrical vanes that close when there is not enough head and reopen when enough flow of water is assured. In stormy weather the structure sinks to a standby low profile by letting out the air of the air pockets.
Most of the kinetic energy of the incoming wave is cancelled by the vertical component of the ramp to push over the upper edge of the ramp from where the water falls to a lower level in the reservoir to a lower potential energy. This amounts to lower efficiency in the process of conversion of the wave's energy. If somehow, the top of the ramp could be continuously adjusted with the water level inside the reservoir, this would always be the optimum level over which the water in the wave will spill.
If also somehow the gap between the waves could be bridged, a continuous flow of water into the reservoir would keep up with the continuous demand of the turbine and the big buffering reservoir won't be necessary.
A more efficient less expensive structure would assure the continuous functioning of the already described water turbine generator group. The proposed invention solves these problems.
The invention assures the conversion of the kinetic and potential wave energy in a continuous flow of water feeding a water turbine.
Finally, the present invention is a significant improvement over U.S. Pat. No. 7,834,475, which was issued to Dan Nicolas Costas, a named inventor of the present invention. The present invention is able to collect significantly more water into the flow that is powering the turbines by allowing the side wave that is in the vicinity of the apparatus to enter the system as it travels along it, in addition to the portion of the wave front that hits the device frontally, and by accepting water from the top as well as from the bottom. Additionally, the present invention is simpler and less expensive to build due to the flap grid combination working as one way valves. Finally, the present invention may be modular and standardized and would therefore less expensive and easier to service.